Multilayer glass ceramic substrate and process for producing the same

ABSTRACT

A multilayer glass ceramic substrate having a plurality of conductor layers each laminated through a glass ceramic layer. The glass ceramic layer has a composition comprising of alumina, borosilicate magnesium glass and cordierite crystal produced by chemical reaction between alumina and borosilicate magnesium glass. The content of alumina is 12 to 59.6 wt %, the content of borosilicate magnesium glass is 18 to 69.6 wt %, the content of the cordierite crystal is 1 to 50 wt % and the sum of components is 100 wt %. The multilayer glass ceramic substrate shows improved mechanical strength.

This is a division of Ser. No. 08/846,820 filed Apr. 30, 1997, now U.S. Pat. No. 5,753,376; which was a continuation of Ser. No. 08/513,668, Aug. 4, 1995, abandoned, which is a continuation of Ser. No. 08/073,725 Jun. 8, 1993 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer glass ceramic substrate used for high density implementation of LSI elements and more specifically to a multilayer glass ceramic substrate which can be sintered at low temperatures and to a process for producing the same.

2. Description of the Related Arts

Development of semiconductor technology require down-sizing and high-speed of electronics devices and systems. In fact, as the semiconductor elements are integrated into VLSI and ULSI of high density, very high density and fine-processing are required in the implementation technique for assembling the elements. In particular, it is requested to increase the wiring density of the substrate on which semiconductor elements are implemented so as to comply with finer pattering and higher operation speed and to lower the dielectric constant of substrate materials.

Alumina multilayer substrate has been used widely. This substrate is produced by a thick film printed multilayer technique or a green sheet lamination technique. The latter technique is more advantageous so as to satisfy requirement of high-density integration. In the green sheet lamination technique, a plurality of thin ceramic green sheets each on which wiring lines are printed are laminated before integrated, so that it is easy to increase the wiring layers to a desired number and hence the wiring density can be increased comparing to the thick film printed multilayer technique.

Alumina ceramic, however, has such a demerit that sintering must be carried out above 1,500° C. which require to use, as wiring conductor, Mo, W metal having a relatively high electric resistance and hence it is difficult to realize fine wiring. Still more, the dielectric constant of alumina is about 10 which is too high for high-speed operation of signals.

Recently, ceramic materials which can be sintered at relatively lower temperatures have been developed so that low resistance conductors such as Au, Ag--Pd, Ag or Cu can be used. For example, a composite material consisting of alumina and borosilicate lead glass can be sintered at a low temperature below 1,000° C. to produce a multilayer substrate in which Au, Ag--Pd or Ag can be used as a wiring conductor. However, in this composite material, it is difficult to use wiring of Cu which is a base metal because the composite material contains lead and hence sintering can not be carried out in a reduction atmosphere. Still more, the electric constant of this composite material can not be lowered below 7.5.

Glass ceramic material using borosilicate glass is also know. This glass ceramic material can be sintered at a temperature lower than 1,000° C. in a reduction atmosphere and has lower dielectric constant of about 5.5, so that a multilayered structure having wiring lines of Cu can be realized simultaneously at the sintering of glass ceramic. Known glass ceramic material, however, possess very poor mechanical strength because no crystallization occur by the sintering.

The mechanical strength is a very important factor of the substrate. In fact, in the case of a multi-chip implementation substrate on which a large number of semiconductor elements are implemented, the substrate size increases and input/output terminals or pins are connected at different levels, if the he mechanical strength of the substrate is poor, problems of breakage of the substrate, junction failure or the like occur in assembly stage and on a product.

An object of the present invention is to resolve the problems of conventional implementation substrate and to provide a multilayer glass ceramic substrate which can be sintered at a low temperature below 1,000° C. in neutral and reduction atmosphere in addition to oxidation atmosphere and which has a low dielectric constant and improved mechanical strength.

The multilayer glass ceramic substrate according to the present invention can be used as an implementation substrate for high-density fine-wiring and high speed, since low resistance metals such as Au, Ag, Cu, Ag--Pd or the like can be used as wiring conductor.

SUMMARY OF THE INVENTION

The present invention provides a multilayer glass ceramic substrate having a plurality of conductor layers each laminated through a glass ceramic layer, characterized in that the glass ceramic layer has a composition comprising of alumina, borosilicate magnesium glass and cordierite crystal produced by chemical reaction between alumina and borosilicate magnesium glass, the content of alumina being 12 to 59.6 wt %, the content of borosilicate magnesium glass being 18 to 69.6 wt % and the content of the cordierite crystal being 1 to 50 wt %, the sum of components being 100 wt %.

The composition can contain a forth component selected from a group consisting of silica glass, α-quartz and mullite. The content of the forth component is 10 to 30 wt %, the sum of components being 100 wt %.

The present invention provides also a process for producing a multilayer glass ceramic substrate by the steps of mixing material powders, preparing green sheets from slurry of the mixed material powders, forming via halls in the green sheets, printing wiring conductors on the green sheets and filling the via halls with conductor, laminating a plurality printed sheets, compressing the laminated sheets under heat and then sintering compressed sheets at a temperature below 1,000° C., characterized in that the mixed material powders consist of 30 to 60 wt % of alumina powder and 70 to 40 wt % of borosilicate magnesium glass powder.

In the process according to the present invention, cordierite crystals are produce when alumina powder and borosilicate magnesium glass powder are sintered.

Alumina powder has preferably the average particle size of 0.5 to 3 μm and borosilicate magnesium glass powder has preferably the average particle size of 1 to 5 μm.

In a variation of the process according to the present invention, a third powder selected from a group consisting of silica glass, α-quartz and mullite is added to the material powders in such proportions as 10 to 50 wt % of alumina powder, 40 to 70 wt % of borosilicate magnesium glass powder and 10 to 50 wt % of the third powder, the sum of all powders being 100 wt %.

The third powder has preferably the average particle size of 0.5 to 10 μm.

The content of magnesium in the borosilicate magnesium glass is preferably more than 5 wt % in term of magnesium oxide.

In the process according to the present invention, the material powders or green sheets are sintered below 1,000° C. to produce a multilayer glass ceramic substrate having improved properties because of following reason. In the sintering, borosilicate magnesium glass start to be softened at about 700° C. The resulting liquidized glass penetrate into and fill in spaces or clearances among ceramic powders of alumina, among ceramic powders of alumina and cordierite crystals and among ceramic powders of alumina, cordierite crystals and silica glass, α-silica or mullite to produce packed structure and a completely compacted glass ceramic body is formed finally at a temperature range form 800 to 1,000° C.

The material powders or green sheets of the present invention can be sintered in a reduction atmosphere because the material powders of the present invention do not contain such element that is reduced to elemental metal from oxide under the sintering condition. To the contrary, in the case of known material powders containing for example lead oxide, lead oxide is converted, in the reduction atmosphere, to metal lead which seriously deteriorate the insulation property of the resulting glass ceramic body obtained.

The multilayer glass ceramic substrate according to the present invention possesses improved mechanical strength which is one of very important properties required in implementation of semiconductor elements. Usually, the bending strength of higher than 2,000 kg/cm² is required in the substrate for implementing semiconductor elements. The multilayer glass ceramic substrate according to the present invention satisfies this strength because a compacted fine structure is realized by the sintering. In fact, the reaction between alumina and liquidized glass produces the cordierite crystal, so that the resulting glass ceramic obtained by the sintering possess a fine strong structure in which particles of alumina, particles of cordierite crystal (and also particles of quart glass, α-quartz or mullite, if they exist) and glassy mass are bonded three-dimensionally and which has an improved bending strength.

In the process according to the present invention, sintering can be effected below 1,000° C., the multilayer structure can be easily realized by the green sheet lamination technique and any conductor including basic metals such as Cu, Ni, their alloys or those that must be sintered in neutral or reduction atmosphere in addition to noble metals of Au, Ag, Pd, Pt or the like can be used.

The multilayer glass ceramic substrate according to the present invention possesses improved mechanical strength or bending strength of higher than 2,000 kg/cm² and low dielectric constant and makes it possible to realize fine wiring with high implementation density.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, Examples of the present invention is explained but the present invention is not limited to the Examples.

Example 1 (Alumina+Borosilicate Magnesium Glass)

As material powders, alumina powder and borosilicate magnesium glass powder were used.

Alumina powder having the average particle size of 0.5 μm to 3 μm and borosilicate magnesium glass powder having the average particle size of 1 to 5 μm were intimately mixed at a proportion range from 30 wt %:70 wt % to 60 wt %:40 wt %.

Borosilicate magnesium glass used have following composition by weight:

    ______________________________________                                         B.sub.2 O.sub.5                                                                         15            CaO    1                                                SiO.sub.2                                                                               65            BaO    1                                                MgO      12            TiO.sub.2                                                                             1                                                Na.sub.2 O                                                                              2             ZrO.sub.2                                                                             1                                                K.sub.2 O                                                                               2                                                                     ______________________________________                                    

The resulting mixed material powder was dispersed together with an organic binder of polyvinyl butyral, polyvinyl alcohol or polyacrylic resin in a solvent to prepare a slurry from which a green sheet was molded by slip casting technique. The thickness of the green sheet was adjusted in a range from 10 to 400 μm.

Then, via halls connecting upper and lower conductors were formed in the green sheet by a punching machine. A wiring pattern was printed by screen printing technique with conductor past and the via halls were filled with the conductor past. The conductor past used consisted mainly of Au, Ag, Ag--Pd, Cu, Ni or Ag--Pt.

Predetermined numbers of green sheets each on which the conductor pattern was printed and of which the via hall was filled were laminated and compacted under heat. Then, the laminated green sheets were heated to a temperature of 400 to 700° C. to remove the organic binder and the solvent (elimination of binder).

Finally, the laminated green sheets were sintered at a temperature ranging form 800 to 1,000° C. to obtain a multilayer glass ceramic substrate. During this sintering stage, the cordierite crystal is produced by a chemical reaction between alumina and borosilicate magnesium glass and the softened glass mass penetrate into and fill spaces or clearances among particles so as to promote compacted structure.

Composition of glass ceramic layer of sintered substrates obtained are summarized in Table 1. The composition was determined by usual X-ray diffraction method. The contents of alumina and cordierite crystal which are determined by comparing their peaks to a peak of silicon used as a reference and a proportion of borosilicate magnesium glass is calculated by subtracting their contents from the total.

Conductor, sintering conditions, numbers of layers and wiring specification used for manufacturing multilayer glass ceramic substrates as well as the results obtained are summarized in Tables 2 and 3. The sample numbers in Table 1 correspond to those in Tables 2 and 3.

                  TABLE 1                                                          ______________________________________                                         Alumina + borosilicate magnesium glass                                         Composition ratio (wt %)                                                       Sample               Borosilicate                                                                             Cordierite                                      Number  Alumina      glass     crystal                                         ______________________________________                                          1      12           38        50                                               2      12           43        45                                               3      12           48        40                                               4      17.4         32.6      50                                               5      18.1         37.6      44.3                                             6      18.2         50.1      31.7                                             7      22.0         29.1      48.9                                             8      23.2         39.5      37.3                                             9      23.3         48.7      28.0                                            10      23.5         57.3      19.2                                            11      27.9         29.8      42.3                                            12      28.1         41.0      30.9                                            13      28.1         50.5      21.4                                            14      28.3         61.8      9.9                                             15      33.2         18.9      47.8                                            16      33.3         31.6      35.1                                            17      33.3         35.3      31.4                                            18      33.5         46.9      19.6                                            19      38.4         27.7      33.9                                            20      38.4         31.4      30.2                                            21      38.7         34.7      26.6                                            22      38.8         50.7      10.5                                            23      42.0         18.0      40                                              24      42.1         33.8      24.1                                            25      42.1         37.3      20.6                                            26      42.3         43.2      14.5                                            27      46.3         38.2      15.5                                            28      46.3         43.7      10.0                                            29      48.4         18.0      33.6                                            30      48.6         20.9      30.5                                            31      48.7         29.8      21.5                                            32      48.7         35.2      16.1                                            33      52.5         21.8      25.7                                            34      52.5         27.4      20.1                                            35      52.6         30.3      17.1                                            36      52.8         34.1      13.1                                            37      56.1         29.8      14.1                                            38      56.3         33.7      10                                              39      56.3         38.5      5.2                                             40      56.5         42.5      1.0                                             ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________      1  900   Ag   Air   30  120  300                                                                               150   5.4  40      2200 >10.sup.13             2  900   Ag   Air   30  120  300                                                                               150   5.3  41      2300 >10.sup.13             3  910   Ag--Pd                                                                              Air   30  120  300                                                                               150   5.2  43      2300 >10.sup.13             4  880   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  40      2200 >10.sup.13             5  850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  43      2300 >10.sup.13             6  850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.1  46      2600 >10.sup.13             7  900   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.8  40      2300 >10.sup.13             8  910   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.6  44      2300 >10.sup.13             9  900   Ag   Air   40  150  300                                                                               150   5.3  48      2400 >10.sup.13            10  900   Ag   Air   40  150  300                                                                               150   5.0  49      2600 >10.sup.13            11  890   Ag   Air   40  150  300                                                                               200   5.8  43      2700 >10.sup.13            12  880   Ag   Air   40  150  300                                                                               200   5.6  47      2500 >10.sup.13            13  900   Ag--Pd                                                                              Air   40  150  300                                                                               200   5.5  49      2400 >10.sup.13            14  880   Ag--Pd                                                                              Air   30  150  300                                                                               200   5.2  52      2600 >10.sup.13            15  880   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.5  41      2600 >10.sup.13            16  900   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.2  45      2400 >10.sup.13            17  870   Ag   Air   30  100  250                                                                               120   6.2  46      2500 >10.sup.13            18  850   Ag   Air   30  100  250                                                                               120   6.0  49      2500 >10.sup.13            19  890   Ag   Air   30  100  250                                                                               120   6.2  47      2700 >10.sup.13            20  900   Ag   Air   35  100  300                                                                               150   6.1  47      2500 >10.sup.13            __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     21  900   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.1  43      2500 >10.sup.13            22  850   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.8  48      2800 >10.sup.13            23  930   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.8  39      2400 >10.sup.13            24  900   Cu   N.sub.2                                                                              40  150  300                                                                               150   6.1  45      2500 >10.sup.13            25  910   Cu   N.sub.2 + H.sub.2                                                                    40  150  350                                                                               150   5.9  48      2500 >10.sup.13            26  900   Au   Air   40  150  350                                                                               150   5.8  50      2600 >10.sup.13            27  900   Ag   Air   40  150  250                                                                               150   5.8  51      2700 >10.sup.13            28  880   Cu   N.sub.2                                                                              40  150  250                                                                               150   6.2  53      2800 >10.sup.13            29  950   Cu   N.sub.2                                                                              40  120  300                                                                               120   6.7  45      2500 >10.sup.13            30  930   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.6  47      2500 >10.sup.13            31  900   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.4  49      2400 >10.sup.13            32  900   Au   Air   30  120  300                                                                               120   6.2  51      2300 >10.sup.13            33  930   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.7  48      2400 >10.sup.13            34  910   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.5  50      2400 >10.sup.13            35  950   Ag--Pd                                                                              Air   30  120  250                                                                               100   6.4  51      2300 >10.sup.13            36  950   Ag--Pd                                                                              Air   30  100  200                                                                                80   6.4  51      2300 >10.sup.13            37  930   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.7  50      2400 >10.sup.13            38  960   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.5  52      2300 >10.sup.13            39  900   Ag   Air   40  100  250                                                                               120   6.4  54      2200 >10.sup.13            40  900   Cu   N.sub.2                                                                              40   80  200                                                                                80   6.5  55      2100 >10.sup.13            __________________________________________________________________________

Tables 2 and 3 reveal such facts that multilayer glass ceramic substrates having the compositions according to the present invention shown in Table 1 posses improved properties required in practical uses including satisfactory mechanical strength and that fine wiring of high-density can made easily.

On the contrary, when the content of alumina is less than 12 wt %, the bending strength of substrate become lower than 2,000 kg/cm² and is insufficient. If the alumina content exceed 59.6 wt %, sintering can not be carried out below 1,000° C. so that the insulation resistance decrease and that the bending strength become lower than 2,000 kg/cm² and the dielectric constant becomes higher than 7, which is disadvantageous for high-speed circuits. In these cases, practical multilayer glass ceramic substrate can not be produced.

When the content of borosilicate magnesium glass is not higher than 18 wt %, it is impossible to obtain a glass phase sufficient to fill spaces or clearances among alumina particles, so that the strength become lower and the reliability can not be expected. If the content of borosilicate magnesium glass exceed 69.6 wt %, the strength intrinsic to glass dominates so that the bending strength become less than 2,000 kg/cm².

If the content of the cordierite crystal is less than 1 wt %, the effect for reinforcing the strength obtained by the presence of cordierite crystals can not be expected so that it is impossible to obtain the bending strength of more than 2,000 kg/cm². If the content of the cordierite crystal exceed 50 wt %, the multilayer glass ceramic substrate does not shrink uniformly and hence the reliability is lost.

If the content of magnesium in the borosilicate magnesium glass used as a material powder becomes less than 5 wt % in term of magnesium oxide, no or little cordierite crystal is produced by sintering operation.

If the particle size of alumina powder used becomes lower than 0.5 μm or higher than 3 μm, and if the particle size of borosilicate magnesium glass powder become lower than 1 μm or higher than 5 μm, the mixed material powder can not be sintered satisfactorily, so that the resulting multilayer glass ceramic substrate shows very poor reliability and hence can not be used in practical uses.

Example 2 (Alumina+Borosilicate Magnesium Glass+Silica Glass)

Example 1 is repeated except silica glass was added to the material powders of alumina powder and borosilicate magnesium glass powder.

Namely, alumina powder having the average particle size of 0.5 μm to 3 μm, borosilicate magnesium glass powder having the average particle size of 1 to 5 μm and silica glass powder having the average particle size of 0.5 μm to 10 μm were intimately mixed at a proportion of (alumina+silica glass): borosilicate magnesium glass of from 30 wt %:70 wt % to 60 wt %:40 wt %. The proportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained are summarized in Table 4 and conductor, sintering conditions, numbers of layers and wiring specification used for manufacturing multilayer glass ceramic substrates as well as the results obtained are summarized in Tables 5 and 6. The sample numbers in Table 4 correspond to those in Tables 5 and 6.

                  TABLE 4                                                          ______________________________________                                         Alumina + borosilicate magnesium glass + silica glass                          Composition ratio (wt %)                                                       Sample                     Borosilicate type                                                                        Cordierite                                Number Alumina  Silica glass                                                                              Glass     crystal                                   ______________________________________                                         101    12.0     21.0       37.0      30.0                                      102    12.0     30.0       33.0      25.0                                      103    12.4     11.0       69.6      20.0                                      104    17.0     25.0       32.0      26.0                                      105    17.0     10.0       23.0      50.0                                      106    18.0     21.0       40.0      21.0                                      107    22.0     18.0       25.0      35.0                                      108    23.0     15.0       27.0      35.0                                      109    23.0     19.0       38.0      20.0                                      110    23.0     24.0       20.0      33.0                                      111    28.0     20.0       19.0      33.0                                      112    28.0     11.0       51.0      10.0                                      113    28.0     17.0       40.0      15.0                                      114    28.0     17.0       35.0      20.0                                      115    33.0     17.0       36.0      14.0                                      116    33.0     12.0       25.0      30.0                                      117    33.0     18.0       20.0      29.0                                      118    34.0     10.0       45.0      11.0                                      119    38.0     19.0       18.0      25.0                                      120    38.0     24.0       24.0      14.0                                      121    39.0     15.0       28.0      18.0                                      122    39.0     11.0       40.0      10.0                                      123    42.0     11.0       18.0      29.0                                      124    42.0     12.0       28.0      18.0                                      125    42.0     10.0       30.0      18.0                                      126    42.5     13.0       34.5      10.0                                      127    46.0     10.0       31.0      23.0                                      128    46.0     11.0       33.0      10.0                                      129    48.0     11.0       18.0      23.0                                      130    48.0     12.0       21.0      19.0                                      131    49.0     10.0       21.0      20.0                                      132    49.0     15.0       26.0      10.0                                      133    52.0     12.0       18.0      18.0                                      134    52.0     12.0       20.0      16.0                                      135    53.0     11.0       22.0      14.0                                      136    53.0     11.0       24.0      12.0                                      137    56.0     10.0       25.0      9.0                                       138    56.0     10.0       21.0      13.0                                      139    57.0     10.0       24.0      9.0                                       140    59.6     10.0       19.4      11.0                                      ______________________________________                                    

                                      TABLE 5                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     101 900   Ag   Air   30  120  300                                                                               150   5.0  40      2200 >10.sup.13            102 900   Ag   Air   30  120  300                                                                               150   4.9  41      2300 >10.sup.13            103 910   Ag--Pd                                                                              Air   30  120  300                                                                               150   4.8  43      2300 >10.sup.13            104 880   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.1  40      2200 >10.sup.13            105 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  43      2300 >10.sup.13            106 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   4.7  46      2600 >10.sup.13            107 900   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.4  40      2300 >10.sup.13            108 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.2  44      2300 >10.sup.13            109 900   Ag   Air   40  150  300                                                                               150   4.9  48      2400 >10.sup.13            110 900   Ag   Air   40  150  300                                                                               150   4.6  49      2600 >10.sup.13            111 890   Ag   Air   40  150  300                                                                               200   5.4  43      2700 >10.sup.13            112 880   Ag   Air   40  150  300                                                                               200   5.2  47      2500 >10.sup.13            113 900   Ag--Pd                                                                              Air   40  150  300                                                                               200   5.1  49      2400 >10.sup.13            114 880   Ag--Pd                                                                              Air   30  150  300                                                                               200   4.8  52      2600 >10.sup.13            115 880   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.1  41      2600 >10.sup.13            116 900   Ag--Pd                                                                              Air   30  100  200                                                                               100   5.8  45      2400 >10.sup.13            117 870   Ag   Air   30  100  250                                                                               120   5.8  46      2500 >10.sup.13            118 850   Ag   Air   30  100  250                                                                               120   5.6  49      2500 >10.sup.13            119 890   Ag   Air   30  100  250                                                                               120   5.8  47      2700 >10.sup.13            120 900   Ag   Air   35  100  300                                                                               150   5.7  47      2500 >10.sup.13            __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     121 900   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.7  43      2500 >10.sup.13            122 850   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.4  48      2800 >10.sup.13            123 930   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.4  39      2400 >10.sup.13            124 900   Cu   N.sub.2                                                                              40  150  300                                                                               150   5.7  45      2500 >10.sup.13            125 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  350                                                                               150   5.5  48      2500 >10.sup.13            126 900   Au   Air   40  150  350                                                                               150   5.4  50      2600 >10.sup.13            127 900   Ag   Air   40  150  250                                                                               150   5.4  51      2700 >10.sup.13            128 880   Cu   N.sub.2                                                                              40  150  250                                                                               150   5.8  53      2800 >10.sup.13            129 950   Cu   N.sub.2                                                                              40  120  300                                                                               120   6.3  45      2500 >10.sup.13            130 930   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.2  47      2500 >10.sup.13            131 900   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.0  49      2400 >10.sup.13            132 900   Au   Air   30  120  300                                                                               120   5.8  51      2300 >10.sup.13            133 930   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.3  48      2400 >10.sup.13            134 910   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.1  50      2400 >10.sup.13            135 950   Ag--Pd                                                                              Air   30  120  250                                                                               100   6.0  51      2300 >10.sup.13            136 950   Ag--Pd                                                                              Air   30  100  200                                                                                80   6.0  51      2300 >10.sup.13            137 930   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.3  50      2400 >10.sup.13            138 960   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.1  52      2300 >10.sup.13            139 900   Ag   Air   40  100  250                                                                               120   6.0  54      2200 >10.sup.13            140 900   Cu   N.sub.2                                                                              40   80  200                                                                                80   6.1  55      2100 >10.sup.13            __________________________________________________________________________

When the content of silica glass powder is less than 10 wt %, the dielectric constant become higher than 7. On the other hand, if the content of silica glass powder exceed 30 wt %, satisfactory sintering can not be carried out so that the insulation resistance becomes lower and the bending strength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μm or higher than 3 μm, the particle size of borosilicate magnesium glass powder become lower than 1 μm or higher than 5 μm and the particle size of silica glass powder become lower than 0.5 μm or higher than 10 μm, the mixed material powder can not be sintered satisfactorily, so that the resulting multilayer glass ceramic substrate shows very poor reliability and hence can not be used in practical uses.

By the same reason as Example 1, practical multilayer glass ceramic substrate can not be obtained outside the proportions according to the present invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % of borosilicate magnesium glass and higher than 1 wt % of cordierite crystal).

By the same reason as Example 1, if the content of magnesium in the borosilicate magnesium glass used becomes less than 5 wt % in term of magnesium oxide, no or little cordierite crystal is produced by sintering operation.

Example 3 (Alumina+Borosilicate Magnesium Glass+Mullite)

Example 2 is repeated except silica glass was replaced by mullite powder.

Namely, alumina powder, borosilicate magnesium glass powder and mullite powder having the average particle size of 0.5 μm to 10 μm were intimately mixed at a proportion of (alumina+mullite): borosilicate magnesium glass of from 30 wt %:70 wt % to 60 wt %:40 wt %. The proportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained are summarized in Table 7 and conductor, sintering conditions, numbers of layers and wiring specification used for manufacturing multilayer glass ceramic substrates as well as the results obtained are summarized in Tables 8 and 9. The sample numbers in Table 7 correspond to those in Tables 8 and 9.

                  TABLE 7                                                          ______________________________________                                         Alumina + borosilicate magnesium glass + mullite                               Composition ratio (wt %)                                                       Sample                    Borosilicate type                                                                         Cordierite                                Number Alumina   Mullite  Glass      crystal                                   ______________________________________                                         201    12.0      21.0     37.0       30.0                                      202    12.0      30.0     33.0       25.0                                      203    12.4      11.0     69.6       20.0                                      204    17.0      25.0     32.0       26.0                                      205    17.0      10.0     23.0       50.0                                      206    18.0      21.0     40.0       21.0                                      207    22.0      18.0     25.0       35.0                                      208    23.0      15.0     27.0       35.0                                      209    23.0      19.0     38.0       20.0                                      210    23.0      24.0     20.0       33.0                                      211    28.0      20.0     19.0       33.0                                      212    28.0      11.0     51.0       10.0                                      213    28.0      17.0     40.0       15.0                                      214    28.0      17.0     35.0       20.0                                      215    33.0      17.0     36.0       14.0                                      216    33.0      12.0     25.0       30.0                                      217    33.0      18.0     20.0       29.0                                      218    34.0      10.0     45,0       11.0                                      219    38.0      19.0     18.0       25.0                                      220    38.0      24.0     24.0       14.0                                      221    39.0      15.0     28.0       18.0                                      222    39.0      11.0     40.0       10.0                                      223    42.0      11.0     18.0       29.0                                      224    42.0      12.0     28.0       18.0                                      225    42.0      10.0     30.0       18.0                                      226    42.5      13.0     34.5       10.0                                      227    46.0      10.0     31.0       23.0                                      228    46.0      11.0     33.0       10.0                                      229    48.0      11.0     18.0       23.0                                      230    48.0      12.0     21.0       19.0                                      231    49.0      10.0     21.0       20.0                                      232    49.0      15.0     26.0       10.0                                      233    52.0      12.0     18.0       18.0                                      234    52.0      12.0     20.0       16.0                                      235    53.0      11.0     22.0       14.0                                      236    53.0      11.0     24.0       12.0                                      237    56.0      10.0     25.0       9.0                                       238    56.0      10.0     21.0       13.0                                      239    57.0      10.0     24.0       9.0                                       240    59.6      10.0     19.4       11.0                                      ______________________________________                                    

                                      TABLE 8                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     201 900   Ag   Air   30  120  300                                                                               150   5.4  40      2200 >10.sup.13            202 900   Ag   Air   30  120  300                                                                               150   5.3  41      2300 >10.sup.13            203 910   Ag--Pd                                                                              Air   30  120  300                                                                               150   5.2  43      2300 >10.sup.13            204 880   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  40      2200 >10.sup.13            205 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  43      2300 >10.sup.13            206 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.1  46      2600 >10.sup.13            207 900   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.8  40      2300 >10.sup.13            208 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.6  44      2300 >10.sup.13            209 900   Ag   Air   40  150  300                                                                               150   5.3  48      2400 >10.sup.13            210 900   Ag   Air   40  150  300                                                                               150   5.0  49      2600 >10.sup.13            211 890   Ag   Air   40  150  300                                                                               200   5.8  43      2700 >10.sup.13            212 880   Ag   Air   40  150  300                                                                               200   5.6  47      2500 >10.sup.13            213 900   Ag--Pd                                                                              Air   40  150  300                                                                               200   5.5  49      2400 >10.sup.13            214 880   Ag--Pd                                                                              Air   30  150  300                                                                               200   5.2  52      2600 >10.sup.13            215 880   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.5  41      2600 >10.sup.13            216 900   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.2  45      2400 >10.sup.13            217 870   Ag   Air   30  100  250                                                                               120   6.2  46      2500 >10.sup.13            218 850   Ag   Air   30  100  250                                                                               120   6.0  49      2500 >10.sup.13            219 890   Ag   Air   30  100  250                                                                               120   6.2  47      2700 >10.sup.13            220 900   Ag   Air   35  100  300                                                                               150   6.1  47      2500 >10.sup.13            __________________________________________________________________________

                                      TABLE 9                                      __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     221 900   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.1  43      2500 >10.sup.13            222 850   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.8  48      2800 >10.sup.13            223 930   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.8  39      2400 >10.sup.13            224 900   Cu   N.sub.2                                                                              40  150  300                                                                               150   6.1  45      2500 >10.sup.13            225 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  350                                                                               150   5.9  48      2500 >10.sup.13            226 900   Au   Air   40  150  350                                                                               150   5.8  50      2600 >10.sup.13            227 900   Ag   Air   40  150  250                                                                               150   5.8  51      2700 >10.sup.13            228 880   Cu   N.sub.2                                                                              40  150  250                                                                               150   6.2  53      2800 >10.sup.13            229 950   Cu   N.sub.2                                                                              40  120  300                                                                               120   6.7  45      2500 >10.sup.13            230 930   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.6  47      2500 >10.sup.13            231 900   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.4  49      2400 >10.sup.13            232 900   Au   Air   30  120  300                                                                               120   6.2  51      2300 >10.sup.13            233 930   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.7  48      2400 >10.sup.13            234 910   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.5  50      2400 >10.sup.13            235 950   Ag--Pd                                                                              Air   30  120  250                                                                               100   6.4  51      2300 >10.sup.13            236 950   Ag--Pd                                                                              Air   30  100  200                                                                                80   6.4  51      2300 >10.sup.13            237 930   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.7  50      2400 >10.sup.13            238 960   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.5  52      2300 >10.sup.13            239 900   Ag   Air   40  100  250                                                                               120   6.4  54      2200 >10.sup.13            240 900   Cu   N.sub.2                                                                              40   80  200                                                                                80   6.5  55      2100 >10.sup.13            __________________________________________________________________________

When the content of mullite powder is less than 10 wt %, the dielectric constant become higher than 7. On the other hand, if the content of mullite powder exceed 30 wt %, satisfactory sintering can not be carried out so that the insulation resistance becomes lower and the bending strength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μm or higher than 3 μm, the particle size of borosilicate magnesium glass powder become lower than 1 μm or higher than 5 μm and the particle size of mullite powder become lower than 0.5 μm or higher than 10 μm, the mixed material powder can not be sintered satisfactorily, so that the resulting multilayer glass ceramic substrate shows very poor reliability and hence can not be used in practical uses.

By the same reason as Example 2, practical multilayer glass ceramic substrate can not be obtained outside the proportions according to the present invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % of borosilicate magnesium glass and higher than 1 wt % of cordierite crystal).

By the same reason as Example 2, if the content of magnesium in the borosilicate magnesium glass used becomes less than 5 wt % in term of magnesium oxide, no or little cordierite crystal is produced by sintering operation.

Example 4 (Alumina+Borosilicate Magnesium Glass+α-quartz)

Example 2 is repeated except silica glass was replaced by α-quartz powder.

Namely, alumina powder, borosilicate magnesium glass powder and α-quartz powder having the average particle size of 0.5 μm to 10 μm were intimately mixed at a proportion of (alumina+α-quartz): borosilicate magnesium glass of from 30 wt %:70 wt % to 60 wt %:40 wt %. The proportion of alumina powder was adjusted above 10 wt %.

Composition of glass ceramic layer of sintered substrates obtained are summarized in Table 10 and conductor, sintering conditions, numbers of layers and wiring specification used for manufacturing multilayer glass ceramic substrates as well as the results obtained are summarized in Tables 11 and 12. The sample numbers in Table 10 correspond to those in Tables 11 and 12.

                  TABLE 10                                                         ______________________________________                                         quartza + borosilicate magnesium glass + α                               Composition ratio (wt %)                                                       Sample                    Borosilicate type                                                                         Cordierite                                Number Alumina  α-quartz                                                                           Glass      crystal                                   ______________________________________                                         301    12.0     21.0      37.0       30.0                                      302    12.0     30.0      33.0       25.0                                      303    12.4     11.0      69.6       20.0                                      304    17.0     25.0      32.0       26.0                                      305    17.0     10.0      23.0       50.0                                      306    18.0     21.0      40.0       21.0                                      307    22.0     18.0      25.0       35.0                                      308    23.0     15.0      27.0       35.0                                      309    23.0     19.0      38.0       20.0                                      310    23.0     24.0      20.0       33.0                                      311    28.0     20.0      19.0       33.0                                      312    28.0     11.0      51.0       10.0                                      313    28.0     17.0      40.0       15.0                                      314    28.0     17.0      35.0       20.0                                      315    33.0     17.0      36.0       14.0                                      316    33.0     12.0      25.0       30.0                                      317    33.0     18.0      20.0       29.0                                      318    34.0     10.0      45.0       11.0                                      319    38.0     19.0      18.0       25.0                                      320    38.0     24.0      24.0       14.0                                      321    39.0     15.0      28.0       18.0                                      322    39.0     11.0      40.0       10.0                                      323    42.0     11.0      18.0       29.0                                      324    42.0     12.0      28.0       18.0                                      325    42.0     10.0      30.0       18.0                                      326    42.5     13.0      34.5       10.0                                      327    46.0     10.0      31.0       23.0                                      328    46.0     11.0      33.0       10.0                                      329    48.0     11.0      18.0       23.0                                      330    48.0     12.0      21.0       19.0                                      331    49.0     10.0      21.0       20.0                                      332    49.0     15.0      26.0       10.0                                      333    52.0     12.0      18.0       18.0                                      334    52.0     12.0      20.0       16.0                                      335    53.0     11.0      22.0       14.0                                      336    53.0     11.0      24.0       12.0                                      337    56.0     10.0      25.0       9.0                                       338    56.0     10.0      21.0       13.0                                      339    57.0     10.0      24.0       9.0                                       340    59.6     10.0      19.4       11.0                                      ______________________________________                                    

                                      TABLE 11                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     301 900   Ag   Air   30  120  300                                                                               150   5.0  40      2200 >10.sup.13            302 900   Ag   Air   30  120  300                                                                               150   4.9  41      2300 >10.sup.13            303 910   Ag--Pd                                                                              Air   30  120  300                                                                               150   4.8  43      2300 >10.sup.13            304 880   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.1  40      2200 >10.sup.13            305 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   5.5  43      2300 >10.sup.13            306 850   Cu   N.sub.2                                                                              30  120  250                                                                               120   4.7  46      2600 >10.sup.13            307 900   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.4  40      2300 >10.sup.13            308 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  300                                                                               150   5.2  44      2300 >10.sup.13            309 900   Ag   Air   40  150  300                                                                               150   4.9  48      2400 >10.sup.13            310 900   Ag   Air   40  150  300                                                                               150   4.6  49      2600 >10.sup.13            311 890   Ag   Air   40  150  300                                                                               200   5.4  43      2700 >10.sup.13            312 880   Ag   Air   40  150  300                                                                               200   5.2  47      2500 >10.sup.13            313 900   Ag--Pd                                                                              Air   40  150  300                                                                               200   5.1  49      2400 >10.sup.13            314 880   Ag--Pd                                                                              Air   30  150  300                                                                               200   4.8  52      2600 >10.sup.13            315 880   Ag--Pd                                                                              Air   30  100  200                                                                               100   6.1  41      2600 >10.sup.13            316 900   Ag--Pd                                                                              Air   30  100  200                                                                               100   5.8  45      2400 >10.sup.13            317 870   Ag   Air   30  100  250                                                                               120   5.8  46      2500 >10.sup.13            318 850   Ag   Air   30  100  250                                                                               120   5.6  49      2500 >10.sup.13            319 890   Ag   Air   30  100  250                                                                               120   5.8  47      2700 >10.sup.13            320 900   Ag   Air   35  100  300                                                                               150   5.7  47      2500 >10.sup.13            __________________________________________________________________________

                                      TABLE 12                                     __________________________________________________________________________                          Number                                                                             Size of Wire       Coefficient                            Sintering        of  Wire Wire                                                                              Via   Specific                                                                            of Thermal                                                                             Breaking                                                                            Insulation            Sample                                                                             Temperature                                                                               Sintering                                                                            Layers                                                                             Width                                                                               Pitch                                                                             Diameter                                                                             Inductive                                                                           Expansion                                                                              Strength                                                                            Resistance            No  (° C.)                                                                        Conductor                                                                           Atmosphere                                                                           (Layer)                                                                            (μm)                                                                             (μm)                                                                           (μm)                                                                              Capacity                                                                            (× 10.sup.-7                                                             deg.sup.-1)                                                                            (kg/cm.sup.2)                                                                       (Ω-cm)          __________________________________________________________________________     321 900   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.7  43      2500 >10.sup.13            322 850   Cu   N.sub.2                                                                              35  100  300                                                                               150   5.4  48      2800 >10.sup.13            323 930   Cu   N.sub.2                                                                              35  100  300                                                                               150   6.4  39      2400 >10.sup.13            324 900   Cu   N.sub.2                                                                              40  150  300                                                                               150   5.7  45      2500 >10.sup.13            325 910   Cu   N.sub.2 + H.sub.2                                                                    40  150  350                                                                               150   5.5  48      2500 >10.sup.13            326 900   Au   Air   40  150  350                                                                               150   5.4  50      2600 >10.sup.13            327 900   Ag   Air   40  150  250                                                                               150   5.4  51      2700 >10.sup.13            328 880   Cu   N.sub.2                                                                              40  150  250                                                                               150   5.8  53      2800 >10.sup.13            329 950   Cu   N.sub.2                                                                              40  120  300                                                                               120   6.3  45      2500 >10.sup.13            330 930   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.2  47      2500 >10.sup.13            331 900   Ag--Pd                                                                              Air   30  120  300                                                                               120   6.0  49      2400 >10.sup.13            332 900   Au   Air   30  120  300                                                                               120   5.8  51      2300 >10.sup.13            333 930   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.3  48      2400 >10.sup.13            334 910   Cu   N.sub.2                                                                              30  120  250                                                                               100   6.1  50      2400 >10.sup.13            335 950   Ag--Pd                                                                              Air   30  120  250                                                                               100   6.0  51      2300 >10.sup.13            336 950   Ag--Pd                                                                              Air   30  100  200                                                                                80   6.0  51      2300 >10.sup.13            337 930   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.3  50      2400 >10.sup.13            338 960   Ag--Pd                                                                              Air   40  100  250                                                                               120   6.1  52      2300 >10.sup.13            339 900   Ag   Air   40  100  250                                                                               120   6.0  54      2200 >10.sup.13            340 900   Cu   N.sub.2                                                                              40   80  200                                                                                80   6.1  55      2100 >10.sup.13            __________________________________________________________________________

When the content of α-quartz powder is less than 10 wt %, the dielectric constant become higher than 7. On the other hand, if the content of α-quartz powder exceed 30 wt %, satisfactory sintering can not be carried out so that the insulation resistance becomes lower and the bending strength become lower than 2,000 kg/cm².

When the particle size of alumina powder used becomes lower than 0.5 μm or higher than 3 μm, the particle size of borosilicate magnesium glass powder become lower than 1 μm or higher than 5 μm and the particle size of α-quartz powder become lower than 0.5 μm or higher than 10 μm, the mixed material powder can not be sintered satisfactorily, so that the resulting multilayer glass ceramic substrate shows very poor reliability and hence can not be used in practical uses.

By the same reason as Example 2, practical multilayer glass ceramic substrate can not be obtained outside the proportions according to the present invention (12 to 59.6 wt % of alumina, 18 to 69.6 wt % of borosilicate magnesium glass and higher than 1 wt % of cordierite crystal).

By the same reason as Example 2, if the content of magnesium in the borosilicate magnesium glass used becomes less than 5 wt % in term of magnesium oxide, no or little cordierite crystal is produced by sintering operation. 

We claim:
 1. A process for producing a multilayer glass ceramic substrate by the steps of mixing material powders, preparing green sheets from slurry of the mixed material powders, forming via halls in said green sheets, printing wiring conductors on said green sheets and filling said via halls with conductor, laminating a plurality printed sheets, compressing the laminated sheets under heat and then sintering compressed sheets at a temperature below 1,000° C., characterized in that said mixed material powders consist of 30 to 60 wt % of alumina powder and 70 to 40 wt % of borosilicate magnesium glass powder.
 2. The process set forth in claim 1 wherein alumina powder has the average particle size of 0.5 to 3 μm and borosilicate magnesium glass powder has the average particle size of 1 to 5 μm.
 3. The process set forth in claim 2 wherein the content of magnesium in said borosilicate magnesium glass is more than 5 wt % in term of magnesium oxide.
 4. The process set forth in claim 1 wherein a third powder selected from a group consisting of quartz glass, α-quartz and mullite is added to said material powders in such proportions as 10 to 50 wt % of alumina powder, 40 to 70 wt % of borosilicate magnesium glass powder and 10 to 50 wt % of said third powder, the sum of all powders being 100 wt %.
 5. The process set forth in claim 4 wherein the content of magnesium in said borosilicate magnesium glass is more than 5 wt % in term of magnesium oxide.
 6. The process set forth in claim 1 wherein said third powder has the average particle size of 0.5 to 10 μm.
 7. The process set forth in claim 6 wherein the content of magnesium in said borosilicate magnesium glass is more than 5 wt % in term of magnesium oxide.
 8. The process set forth in claim 1 wherein the content of magnesium in said borosilicate magnesium glass is more than 5 wt % in term of magnesium oxide. 